Step 1: Buy The Stuff

Basics

Raspberry Pi Computer ~ £25

Power ~ £5 - £30

Connect your RPI to power from the mains with one of
these; if you wish to make your AirPi portable, you can attach a rechargeable battery pack such as
this one.
Alternatively, you could power it from a solar panel in
your garden.

Internet

An internet connection can be supplied either via an Ethernet cable or a simple USB WiFi adapter
which you plug directly into the Pi.

We strongly recommend connecting your Pi to the internet, otherwise you won't be able to upload any
of your pi's data and view it remotely.

Screen - optional

You may want a screen to connect to your AirPi in order to view its measurements while offline. Note
that the AirPi can be configured to start automatically and upload data to the internet as soon as it
is switched on, so a screen is not necessary to control it.

Electronics

Breadboards ~ £3

These are a must: you plug your sensors into breadboards to make the necessary circuits. They're
reusable and you can purchase them relatively inexpensively from Oomlout, or any other electronics
supplier.

The number you will need will vary depending on how many sensors you are connecting to your AirPi.
We recommend starting with 1, and adding another for every 3 sensors you will use (For example, with 6
sensors you'd need 3 breadboards).

Wires ~ £3

You will need a fair number of wires to plug into the breadboard to hook up all the sensors. One
option is to buy a roll of wire and a wire stripper, and roll your own. This ends up being cheaper in
the long run, but for this project you can buy a package of many different coloured and different
length jumper wires (recommended) from Oomlout.

Connecting the Pi to your breadboards ~ £5

There are two ways to go about this, either via Adafruit's spectacular Cobbler (which does require soldering together, but makes
life a lot easier afterwards), or by manually connecting the pins on the Pi to the breadboard with
these female-to-female
jumper leads.

Resistors ~ £0.50 or £7.50 for 500

You will need several resistors for different purposes in this project, they will be of different
values depending on which sensors you are using; for example, to protect LEDs, or to control what
voltage the sensors receive from the Pi.

You can either purchase a kit of resistors which should contain all the ones you need here or you can
buy them individually from Maplin or another electronics supplier.

Many of the sensors used in this project output an analogue signal. The Raspberry Pi cannot read
these signals directly, so to convert these signals to digital, you need an ADC (analogue to digital
converter). I recommend the MCP3008 which has 8 separate analogue inputs, so you only need one in order
to read the values for all your sensors. It can be purchased cheaply from
Farnell in the UK.

LEDs ~ £1 - optional

If you want to run your AirPi headless (without a screen) then you may wish to purchase some
red and green LEDs so your Pi can
tell you once its uploaded data. We used a red LED to indicate a failure (for example, no internet),
and a green one to indicate success.

Weather Sensors

The DHT22 sensor is available in the UK from Proto-Pic in the UK, or sellers
on eBay for less than half the cost, but with longer shipping times. It measures both relative
humidity and temperature, however we discovered that it does not measure temperatures below 0 degrees
Celsius. For this reason, we recommend using the BMP085's temperature sensor (listed below), and only using the DHT22 for its
relative humidity output. The DHT22 sensor is digital, so it doesn't need an ADC.

The BMP085 sensor measures both barometric pressure and temperature. Whilst calibrating the sensors,
we discovered that the BMP08's temperature sensor is slightly more accurate than the DHT22's sensor,
and it goes below 0 degrees as well. This sensor is also digital, and so does not require an ADC. It is
available from Proto-Pic in the UK, or many
different Chinese sellers on
eBay for a third the cost but longer shipping times.

Although this sensor is cheap, it's hard to set up. On top of the ADC, it requires an operational amplifier (available for a pound or two), a capacitor and a number of resistors to function. Last time we checked, it can be bought here.

LDR - Light Level - Requires ADC ~ £1

An LDR (Light Dependant Resistor) is a sensor which changes its resistance depending upon the light
level shining upon it. These are extremely cheap and can be obtained easily from any electronics shop.
The output given is analogue, so you will need an ADC (see above) to convert it to digital.

Gas Sensors

This sensor responds to various gases associated with poor air quality and the presence of smoke
including methane, iso-butane, ethanol and hydrogen. It is available from
RS Components. It consists of a 4 pin canister, 2 of which power the heating element for it (5V), and 2 of
which are the connections to the sensing resistor (its resistance is proportional to the air quality).
However, the output given by this sensor is analogue, so you needs an ADC (see above) to use it
properly.

This sensor measures the concentration of NO2 in the air. It is available for approximately £5 from Component Distributors Inc.
It is packaged in approximately the same form factor as the TGS 2600, with the same connections,
however it is powered by 1.7V, not 5V. Similarly, the output given is analogue so an ADC (see above) is
needed to use it.